Currently, as multimedia transmission services, such as VOD (video on demand) or video phones, are becoming widely available, monitoring transmission quality, which has traditionally been performed on a receiver in order to detect errors of transmitted multimedia data, is becoming an important issue. Particularly, in multimedia data service through wireless communication channels which have high error occurrence rates, it is important to control errors by monitoring transmission quality in order to provide reliable picture transmission service.
In wireless communications, the degrees of distortion and error occurrence in received multimedia data vary depending on the location of a receiver. When the transmission quality of multimedia data is not satisfactory at a receiver, customers may be unsatisfied and it is meaningless to continue transmitting such low-quality multimedia data through a noisy channel. Therefore, when a transmitter transmits multimedia data, it is necessary to take proper measures for improving transmission reliability.
Video quality monitoring methods include a FR (full-reference) method, a RR (reduced-reference) method, and a NR (noreference) method.
The full-reference method is known as the most accurate method for measuring video quality because it uses both reference (source) video and processed video sequences. However, since the full-reference method requires the reference video, its application area is limited.
In the reduced-reference method, a set of parameters are extracted from a reference video sequence and the set of extracted parameters is transmitted to a receiver along with video data. At the receiver, another set of parameters is extracted from the received video data and video quality is measured by comparing the two sets of parameters. However, a disadvantage of the reduced-reference method is that an additional bandwidth is required for a downlink channel since additional parameters must be transmitted.
The NR (no-reference) method is used to estimate video quality by analyzing a bit stream contained in MPEG-2 TS (Moving Picture Experts Group-2 Transport Stream). Since, in the no-reference method, video quality is measured by using only decoded processed video sequences without any information on reference video sequences, a disadvantage of the no-reference method is that the accuracy of this method is poor compared to accuracy of the other methods.
Meanwhile, bandwidths are a very important resource in communication systems. In particular, since the bandwidth is limited and expensive in wireless communication systems, it is necessary to minimize additional bandwidths required for monitoring video quality at a receiver.
Although a receiver may measure video quality using a no-reference method in order to minimize additional bandwidth, it is very difficult and inaccurate because the method does not use the reference video sequence. On the other hand, a reduced-reference method has a limitation in that an additional bandwidth is needed.
Furthermore, in order to measure errors occurring during transmission at the receiver, information on the reference video sequence is needed, thus consuming a channel resource.